Mariner 1969 television image processing

Abstract

Mariners 6 and 7 sent back approximately two hundred photographs of Mars, taken from distances ranging between one million and three thousand km relative to the planet surface. These images contain true object space information distorted, to one extent or another, by the signature of the imaging system itself. In order to maximize the scientific yield of the television data, the natures of the distortions introduced by the imaging system must be quantitatively determined, and techniques developed whereby they can be accurately removed.

Television systems typically exhibit photometric nonuniformities and nonlinearities, geometric distortions, both optical and electronic, image retention and spatial frequency response limitations. In addition, Mariner 1969 specific problems were introduced in the course of on-board processing applied in the interest of data compression and efficient bandwidth utilization. A cubing amplifier and an automatic gain control circuit were employed, with photometric “DC reference” supplied in the form of a separately encoded, under sampled raw signal. The effects of on-board processing can in principle be removed by means of combining these separate data streams.

Digital image processing techniques have been developed at the Jet Propulsion Laboratory which enable us to characterize these various distortions using calibration data, and to remove them from images returned by the two Mariner spacecraft. This paper will provide brief descriptions of some of these techniques and illustrations of their application to Mariner 1969 image data.